The invention relates to an elastic coupling of disc construction, and particularly such a coupling of the kind in which one coupling half is comprised of a central disc that is associated with a hub, and the other coupling half is comprised of two side discs which are connected to each other to be rotationally fixed together, wherein the two side discs are arranged on either side of the central disc to enclose the latter at its outer circumference. The side discs are able to rotate by a restricted amount relative to the central disc.
Elastic coupling elements connect the side discs and the central disc for damping relative rotation. In one form, the central disc has a plurality of through ports distributed around its circumference, for accommodating the elastic coupling elements. These elements extend out from the opposite sides of the central disc at the ports, and the elements engage in corresponding recesses in the side discs. The side discs, together with the hub, form an inner chamber that houses the central disc. The inner chamber is substantially fluid-tight and it can be filled with fluid.
At least one displacement chamber is provided which is formed by the two coupling halves. The volume of the displacement chamber varies as the coupling halves counter-rotate. The displacement chamber is able to be filled with fluid. It has a throttle opening for the passage of fluid.
Such couplings are used primarily as torsional oscillation dampers. Frequently, they form part of a motor vehicle clutch. However, they can also be used separately from a clutch. They can also serve purely as a connecting component between an internal combustion engine and a load-switching or "power shift" gear unit. The disc-type construction of the elastic coupling affords the advantage that it requires less space so that the engine and the gear unit can be situated close together.
A coupling of the above-described kind is known from British Pat. No. 637,257 (which is equivalent to U.S. Pat. No. 2,337,134).
The inner chamber of this coupling can be filled with a fluid. In the presence of the fluid, the points at which the parts of the coupling slide over each other are lubricated. With the aid of the fluid, torsional oscillation damping can be obtained. For this purpose, the following provision is made in the known coupling. According to FIGS. 6 to 9 of the above British Patent, small cylinder-piston units are arranged on the helical springs. These form displacement chambers with throttle apertures. Owing to the small total volume of these displacement chambers, their damping effect is relatively slight.
According to FIGS. 1 to 4 of the British Patent, in the inner chamber of the coupling, other displacement chambers 20 are formed by means of extensions 18 and plates 43. However, the damping effect of these displacement chambers is also only slight, since these chambers are open toward the hub 10, whereby the fluid which is to be displaced encounters only slight resistance. This is particularly the case when, over time, the coupling has lost some of the fluid and air has penetrated into the coupling. A fluid loss of this kind can never be fully avoided. When the coupling rotates, the air accumulates in the vicinity of the hub, while the fluid occupies the radially outer region of the inner chamber of the coupling, due to centrifugal force.
The above-described coupling has only inadequate means to restrict the torsion angle. One possibility for this consists in the helical springs 17 "becoming a block", i.e. with their coils resting against one another. However, this reduces the working life of the helical springs. Another possibility consists in the radially inner edges of the extensions 18 striking on the plates 43. Finally, the torsion angle of the coupling can also be restricted by the cylinder-piston units reaching their terminal position. In all three cases, despite the presence of damping fluid, there is a danger of hard impacts, since there is predominantly only line contact between components which strike against each other.